1. Field of the Invention
The present invention relates to a method of acidizing a subterranean formation or well bore employing an acidic solution containing a corrosion inhibitor which substantially reduces the corrosive effects of the acidic solution on ferrous and other metals in contact with the acidic solution.
2. Prior Art
Acidizing and fracturing treatments using aqueous acidic solutions commonly are carried out in hydrocarbon-containing subterranean formations penetrated by a well bore to accomplish a number of purposes, one of which is to increase the permeability of the formation. The increase in formation permeability normally results in an increase in the recovery of hydrocarbons from the formation.
In acidizing treatments, aqueous acidic solutions are introduced into the subterranean formation under pressure so that the acidic solution flows into the pore spaces of the formation. The acidic solution reacts with acid-soluble materials contained in the formation which results in an increase in the size of the pore spaces and an increase in the permeability of the formation.
In fracture-acidizing treatments, one or more fractures are produced in the formation and the acidic solution is introduced into the fracture to etch flow channels in the fracture face. The acid also enlarges the pore spaces in the fracture face and in the formation.
The rate at which acidizing fluids react with reactive materials in the subterranean formation is a function of various factors including but not limited to acid concentration, temperature, fluid velocity and the type of reactive material encountered. Whatever the rate of reaction of the acidic solution, the solution can be introduced into the formation only a certain distance before it becomes spent. It is desirable to maintain the acidic solution in a reactive condition for as long a period of time as possible to maximize the permeability enhancement produced by the acidic solution.
A problem associated with acidizing subterranean formations is the corrosion by the acidic solution of the tubular goods in the well bore and the other equipment used to carry out the treatment. The expense of repairing or replacing corrosion damaged equipment is extremely high. The corrosion problem is exacerbated by the elevated temperatures encountered in deeper formations. The increased corrosion rate of the ferrous and other metals comprising the tubular goods and other equipment results in quantities of the acidic solution being neutralized before it ever enters the subterranean formation. The partial neutralization of the acid results in the production of quantities of metal ions which are highly undesirable in the subterranean formation.
Various methods have been proposed to decrease the corrosion problem related to acidizing treatments, however, the corrosion inhibitors employed generally are effective only at temperature levels below about 300.degree. F. It would be desirable to provide a composition and method for acid treating a subterranean formation which overcomes at least some of the corrosion problems resulting from contact of the aqueous acidic treating solutions with ferrous and other metals.
Monroe, et al., U.S. Pat. No. 3,077,454, attempted to address the corrosion problem referred to above by using a corrosion inhibitor that did not include an acetylenic alcohol. According to Monroe, et al., acid corrosion inhibitors which do contain an acetylenic alcohol are promising but the toxicity and cost has held back their wide acceptance.
The inhibitor made by Monroe, et al., was the product of the reaction of several different compounds. However, the corrosion inhibition results obtained by using the Monroe, et al., reaction product, as disclosed by Monroe, et al., in the working examples, showed that the product was not satisfactory as an inhibitor unless it was blended with an acetylenic alcohol (such as propargyl alcohol) or a wetting agent or an acetylenic alcohol and a wetting agent. The best corrosion inhibition results obtained by Monroe, et al., involved a blend of their reaction product with an acetylenic alcohol. Thus Monroe, et al., failed to produce an effective corrosion inhibitor that does not include an acetylenic alcohol.